Atmospheric-pressure plasma that can be stably generated in the atmosphere yields an advantage in that it does not require vacuum equipment, and the development of its stable generation method and application technology is being conducted with enthusiasm.
The present inventors are engaged in the development of material synthesizing technology and deposition technology in the atmosphere among the material process technologies employing atmospheric-pressure plasma generated in a nozzle or capillary tube (here, a tube shaped with a narrowed tip is referred to as a “nozzle” and a straight tube is referred to as a “capillary tube” for differentiation), and have made several proposals in the past.
For example, Patent Document 1 describes technology related to a method for stably maintaining the generation method of atmospheric-pressure plasma in the chemical vapor deposition (hereinafter referred to as “CVD”) using a gas raw material.
Meanwhile, Patent Document 2 and Patent Document 3 relate to atmospheric-pressure plasma material deposition technology of using a metal wire as the raw material. This is a method of vaporizing the metal wire inserted into the nozzle or capillary tube by using plasma, and the details thereof are described below.
The technology described in Patent Document 2 relates to atmospheric-pressure plasma generation technology in a nozzle with an inner diameter of 50 μm or less, and technology of using the foregoing generation technology for depositing a metal or metallic compound material on a low melting point substrate, in which its melting point is 500° C. or less, in dots with a diameter of 1 to 100 μm and in lines with a width of 5 to 50 μm.
Moreover, the technology described in Patent Document 3 uses a capillary tube to deposit a metal or metallic compound as a thin film on a large area of several hundred μm2 or even several cm2 or more on various types of substrates.
The technologies described in Patent Document 2 and Patent Document 3 use the continuously generated high frequency as the plasma excitation source, and the gas temperature of the plasma reaches several thousand degrees locally. Accordingly, wires with a high melting point made of tungsten, molybdenum or the like are suitable as the raw material, and the preparation of the nanoparticles thereof and thin film deposition can be performed efficiently.    [Patent Document 1] Japanese Patent No. 4041878    [Patent Document 2] Japanese Published Unexamined Application No. 2005-262111    [Patent Document 3] International Publication No. 2008/023523    [Patent Document 4] Japanese Published Unexamined Application No. 2008-150703